In his book إبطال القياس والرأي والاستحسان والتقليد والتعليل, Ibn Hazm quotes this hadeeth of the Prophet, peace be upon him,
دعوني ماتركتكم، فإذا أمرتكم بشيئ فأتوا منه مااستطعتم، وإذا نهيتكم عن شيئ فاتركوه
Translation: "Do not bother me with what I left out; when I order you something, do it as best you can, and when I forbid you something, leave it."
He concludes that whatever is not specified in the Quran and the Sunna as mandated or forbidden, is not something to fret over. He says the famous Completion verse, 5:3, confirms it. He comments on it, on page 37, saying, "Whatever is completed, there is no addition to it."
I looked for that hadeeth, but could not find it in those words. I did, however, find this authentic hadeeth, reported by Al-Bukhaari and Muslim, that says the same thing,
عن أبي هريرة قال: قال رسول الله صلى الله عليه وسلم (ذروني ما تركتكم فإنما هلك من كان قبلكم بسؤالهم واختلافهم على أنبيائهم فإذا أمرتكم بشيء فخذوا منه ما استطعتم وإذا نهيتكم عن شيء فانتهوا) صحيح أخرجه البخاري ومسلم
Narrated Abu-Hurayra, "The Messenger of God, peace be upon him said, 'Do not bother me with what I left out. What destroyed those before you was that they asked too many questions and differed over their prophets. So, when I order you something, take from is as much as you can, and when I forbid you something, comply.' "